What would cause spark knock on a cold engine ('91 Escort)?

[RL2000]

My '91 Escort does just fine once the engine is warmed up, and while idling, but if you start it cold and take off driving, when putting load on the engine, you can hear spark knock. This isn't normal is it?

I know being computer controlled with a coil pack (DIS system), there's no way for me to adjust the ignition timing. I don't think this car has a knock sensor either. I don't believe I have an EGR valve either. This is an Escort Pony, so it's about as basic as they come! (Which is why I love working on it so much!)

I have the Haynes manual, and it shows an EGR valve on the 1.9L (which is what this car has), but in real life, there is no EGR valve in sight, at least anywhere near where they show it is in the book. I have searched high and low for it but to no avail.

The car does have 185,000 miles and you can notice a lack of power when the engine is cold. Once warmed up, it runs like a dream though!

Where would I turn to diagnose and fix something like this?

Thanks!!

[AzTumbleweed]

I've never heard of this happening on a cold engine. I'm wondering if it's not something like rod bearings. It's will cost you but try running some high octane gas in it. If it stops then the problems is what you think. But if it continues with high test then it's something else.

[12Ounce]

If you can take and post an image of your engine ... centering on the intake manifold, we may can help you spot the EGR valve. (Which, by the way, there is almost no likelihood that there is any thing wrong with ....)

[chrisanthony]

i'm just going to throw one out there, maybe the sparkplug might be a kind of loose..

[mightymoose_22]

EGR should be easy to find if it is there.... just follow any tubes that lead away from your exhaust manifold or cat converter to anything resembling a valve with a separate vacuum hose attached... bingo! EGR

In all likelihood it will be mounted on the back side of the intake manifold near the throttle body.

[RL2000]

Sorry for the wait!! I was out of town for 4 days over the past week.

Here are some pictures of the engine, focusing on the intake manifold area.

(See attachments)

[mightymoose_22]

It appears that you don't have an EGR after all. It should show in that second picture.
Do you still have the stickers on the bottom of the hood that show emissions info? Is there ant reference to an EGR on them?

Even so... it is not likely to be what is causing the knock. Regarding the knock, if you are due for new plugs anyway I suggest replacing the plugs and wires (and don't just get the cheapest ones). It is regular maintenance anyway and might correct your problem.

[RL2000]

Originally Posted by mightymoose_22

It appears that you don't have an EGR after all. It should show in that second picture.
Do you still have the stickers on the bottom of the hood that show emissions info? Is there ant reference to an EGR on them?

I'm telling ya, I looked high and low for that EGR valve... I searched everything going into the intake, and tried to find it coming out of the exhaust pipe, with no results!

I looked under the hood, and there was no reference to the EGR valve at all... and it even showed all the vacuum lines!

Originally Posted by mightymoose_22

Even so... it is not likely to be what is causing the knock. Regarding the knock, if you are due for new plugs anyway I suggest replacing the plugs and wires (and don't just get the cheapest ones). It is regular maintenance anyway and might correct your problem.

I suppose I could replace the plugs. I think the wires were supposed to be top of the line "lifetime" grade. I just re-gapped the plugs the other day.

[Davescort97]

I might add that incorrect plugs will make it knock, but so will a faulty PCV valve or a vacuum leak. Check the rubber hose running from the PCV to the intake and make note that the 90 degree elbow is known to crack.

[Intuit]

I have a '94 that DOES have all the modern emmissions controls including EGR and have observed the same issue.

It's helpful to know that a vehicle without all the emissions control equipment has the same issue.

It's virtually non-existant in warm weather and particularly bad in really frigid weather. I let it idle for long periods in cold weather to avoid the issue. (but the thermostat bypass valve is bad so we're talking REALLY long idle periods -- but since it has the side-effect of delaying or preventing the expansion-related HGasket failures I've left it alone)

Our area changes fuel additive packages depending on the season so it may help to use STP COmplete Fuel System cleaner coupled with some brand of gasoline different from what you've been using. Mine seems to run more consistently and with less cold weather noise on Marathon/Speedway gasoline additive packages. Get less power with BP (plus I don't like their smell) and inconsistencies with SHell.

Just yesterday I happened to notice a vacuum line half hanging off at the evaporator cannister below the driver-side headlamp. (also an emissions component BTW) So it's WAY too soon to know whether this will address both the rough/inconsistent idle and cold-engine knock under load issues. That line is dry-rotting but only the end that I cut off was severe enough to warrant attention. It was a little too long anyway which probably cause it to jiggle and fail prematurely. It is now cut to proper length.

In past testing, a large vacuum leak, artificallly created by pulling a line causes a quick but stubborn stall. A small vacuum leak can have little effect as the IAC quickly compensates. Pulling the IAC wire harness can have little or no effect depending on atmospheric, engine temp and other conditions. If the engine stalls on an artifically created small vacuum leak but with the IAC working then there could be another leak present somewhere in the system(?) Dave is probably on the right track.

Some others have also reported leaks at the intake manifold. I noticed when pulling my head that most of these bolts were backing-out. (same for exhaust manifold BTW) So it's a good idea to go and retorque those every 60k or so anyway.

[Intuit]

Update: <<Just yesterday I happened to notice a vacuum line half hanging off at the evaporator cannister below the driver-side headlamp. (also an emissions component BTW) So it's WAY too soon to know whether this will address both the rough/inconsistent idle and cold-engine knock under load issues.>>

This did not address the idle issues however a hissing sound (only audible when hot) has developed and this only confirms the presence of a vacuum leak.

The Haynes manual pointed to EGR and/or vacuum leak as probable causes for both the ping under load ("during acceleration") and idle ("loping") issues.

Thus far I haven't been able to easily locate the source of the leak. All visible portions of every line appear to be in good condition. I sprayed silicon lubricant around the EGR area and this may have caused a dead stall. However, repeating the test doesn't produce any consistent results. Definitely idles better when it's more humid or humidity is at 100% (raining,) regardless of temperature.

[denisond3]

I know the -early- 91 Escort 1.9L LX's did have EGR valves, because I have one sitting in my driveway. The EGR tube led straight down behind the engine though, connecting to the downstream side of the cat. converter, just before the joint to the flex pipe.

I know the 92 Escort 1.9L LX's Didnt have EGR valves, because I have a 92 wagon. But it did have two empty connectors in the wiring harness at the firewall, where the EGR control stuff went in 91.

I know the 94 Escort 1.9L LX's Did have EGR valves, since I have one of those also. The EGR tube led from a fitting in the middle of the exhaust manifold (so the manifold heat shield had a round hole in it), around the side of the motor, and into the EGR valve behind the throttle valve.

What year/month was your Escort manufactured? It will say this on the driver's door frame, down low somewhere.

As for what causes the spark knock (which amounts to either running very lean, or the spark being Way Over advanced) when cold I dont know. Be sure there are no holes/cracks in the large air duct leading from the air filter housing into the throttle valve. And you might want try checking/changing your mass air flow sensor (at the end of the air filter housing). I have no solid reason to think this is causing the spark knock, its just that your symptoms are rare, and so are problems with the mass air flow sensor.
It tells the computer how much air is getting into the motor.
My next suggestion would be to check the fuel pressure when the engine is cold, then check it again when the engine is fully warmed, and it isnt knocking under acceleration.

[Intuit]

............As for what causes the spark knock (which amounts to either running very lean, or the spark being Way Over advanced) when cold...............

Thanks for info. '94 1.9L LX manual shift manufacturered 4th quarter of that year; pretty much identical to the '95 model year. There are three major components to the EGR system. EGR Valve Pressure Sensor, EGR Vacuum Selenoid and of course, the EGR Valve itself. The Pressure sensor attaches to the input line for the EGR valve and I guess monitors pulses/input. The Vacuum selenoid attaches between the intake vacuum line and EGR; and is supposed to apply vacuum only at cruise and highway speeds. The vacuum that is applied to the EGR, sucks on a large piston/plunger inside which then opens a valve, introducing exhaust gases into the intake. (this doesn't pass any of the air flow/temp sensors that I am aware of)

Based on the design of the valve, I assume EGR is pretty much an ON/OFF thing or/and applied in pulses. Anyway if EGR is sticking open and too much exhaust gas is being introduced or introduced at idle then that lowers O2 saturation levels... makes the intake harder to burn. Since EGR doesn't run past any sensors and the computer is not expecting it, then theoretically that might create a lean condition just as unmetered air from a vacuum leak would.

Anyway I have a bunch of plugs so I'm going to cap-off a bunch of lines at the intake to see if that makes any difference.

With advanced timing, one should notice more power right ? Nadda noticed here. As I've understood, the engine runs off of factory pre-programmed settings when first started, then switches over to sensor input information (?). Don't know if this is just a timed switch over or whether there is a trigger, such as engine temperature.

Hasn't yet been cold enough to tell how much or whether the cold engine ping has been affected. Mornings are cooler now so should know real soon. But with this most recent fill up I've noticed it "rattles" under load when hot; as if too lean. Only way you'll hear the noise is if accelerating next to a wall where the sound can reverberate back through an open window. Otherwise not audible at all; which is contrary to the cold spark knock under load issue. No lack of power either; good power. Also unlike the "rattle," the cold spark knock under load has a very regular and predictable timing.

Since his late year '91 or possibly '92 vehicle confirmed, has no EGR emissions equipment then whatever is causing this has to be common to both his and mine; hopefully just unmetered air flow. May plug off all vacuum lines at the intake for EGR Vacuum selenoid, PVC, fuel pressure regulator, charcoal cannister and lastly, the brake master cylinder... just to see if or at what point the idle issue ceases. (for others, do ***NOT*** attempt to drive with brake master cylinder vacuum line detatched/disabled)

There is also a sensor that is attached at the intake, but on the firewall side that I am curious about. Tried to satisfy my curiousity some years ago but had trouble removing it. Had settled on what that was awhile ago but don't remember. It's tucked away and difficult to see. Rolling through some old photos it occurs to me there are a few other gasket surfaces at the intake that can be checked, like the piece that the above mentioned sensor and IAC attaches to. Seriously doubt that the EGR gasket is leaking.